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Life cycle assessment of greenhouse gas mitigation benefits of biochar

TitleLife cycle assessment of greenhouse gas mitigation benefits of biochar
Publication TypeThesis
Year of Publication2014
AuthorsCowie, Annette L., and Cowie Alan J.
Academic DepartmentNSW Department of Primary Industries
UniversityUniversity of New England

This studyevaluated the GHG impacts of a range of biochar systems, made from different biomass feedstocks, under different pyrolysis conditions, and applied to different crops. We used life cycle assessment (LCA) to systematically quantify the GHG emissions and removals at each stage of the biochar system life cycle, from procurement of the biomass feedstock, through manufacture of biochar, to application, including transport. The net GHG emissions were calculated for each system, and sensitivity analyses were performed to assess the most critical components of the calculations. To calculate the GHG impacts of biochar, the biochar system was compared with the relevant reference system, representing the conventional use of the biomass, and conventional soil amendments. Besides biochar, the pyrolysis process produces syngas that can be utilised for renewable electricity, replacing fossil fuels. Therefore, avoided fossil fuel emissions are also included in the analysis. Most biochar scenarios examined led to substantial reduction in greenhouse gas emissions. The greatest reduction, 3.2kg CO2-e per kg biochar, was estimated for poultry litter biochar applied to maize. The benefits were greater for biochar applied to maize than to wheat, and were greater for higher than lower temperature biochars. Biochar does not always reduce emissions compared with the reference system: if the biomass would otherwise have gone to a landfill facility with methane capture and electricity generation, the climate change benefits may have been greaterthan using the biomass for biochar. The results are highly sensitive to the assumptions employed, including the reference use of the biomass, so it is critical that LCA is undertaken for each situation in which biochar use is proposed. In some situations biochar will not give the greatest mitigation benefits compared with alternative uses for biomass. In each case the optimal use of biomass should be considered, bearing in mind also other environmental and production objectives.